Usually, communication between user equipments is implemented by means of forwarding by a base station in a cellular communications technology. That is, user equipment communicates with a base station by using an air interface, and the base station forwards user data to a destination node in a network. However, in cellular communications, due to a shortage of radio spectrum resources, how to improve utilization of a spectrum resource has become a research hotspot.
In view of this, a new wireless interface technology, device-to-device (D2D) communication, has been proposed. D2D communication is a new communications technology in which user equipments are allowed to directly communicate with each other by reusing a cell resource. This can increase spectrum efficiency of a cellular communications system, reduce load of a base station, and resolve, to some extent, a problem of a shortage of spectrum resources in a wireless communications system.
Currently, D2D communication supports multicast communication (that is, 1-to-many communication). That is, D2D user equipment (UE) may send D2D data to several UEs in a communication group. Currently, for D2D communication, a main research hotspot is multicast communication. However, in an actual application, there may be a unicast communication (that is, 1-to-1 communication) requirement. That is, one UE communicates with another UE in a D2D communication manner. Under this requirement, how a base station controls user equipments needing to perform unicast D2D communication has become a problem that urgently needs to be resolved.